Computer systems use power supply units that create power signals in two categories: main power signals; and auxiliary power signals. The main power signals are selectively powered-on and powered-off within the power supply, while the auxiliary power signals remained powered-on at all times when the power supply is coupled to an alternating current (AC) power source. Power supplied from the auxiliary power signals operates devices on the motherboard used to detect user requests to wake the computer system (e.g., from one or more low power sleep states) and command powering-off and powering-on of the main power signals.
Some computer systems are programmed to take specific action on AC power loss, such as an automatic re-boot on AC power loss. Computer systems detect loss of AC power by way detecting loss of the auxiliary power signals. However, as power capacities of power supply units has increased, and the efficiency of the circuits on motherboard that draw power from the auxiliary power signals has likewise increased, in some cases the amount of time a motherboard takes to draw down the auxiliary power signal after AC power loss is longer than the AC power loss itself. Thus, the motherboard may not detect that AC power has been lost and restored, and the desired specific action after AC power loss may not take place.